This invention relates to methods for processing semiconductor wafers. More specifically, the invention relates to methods for processing wafers in a hybrid supercritical fluid processing vessel.
Modern VSLI semiconductor processing presents numerous engineering dilemmas. One important issue involves removal of contamination before, during, and after fabrication steps. For example, photoresist strip and residue removal are critical processes in integrated circuit (IC) fabrication. During dielectric etching in a typical integrated circuit fabrication process, undesirable etch residues and/or polymers such as hydrocarbon, fluorocarbon, and/or polymeric residues (e.g. CxHxFxOx) are formed and left on the surfaces and sidewalls of the resulting structures. Such undesirable residues along with the remaining post-etch photoresist must be removed to prevent quality issues in subsequent deposition: process, such as adhesion problems, and/or diffusion contamination.
One common method to remove such residues is plasma stripping; however, plasma stripping is often damaging to advanced low-k materials. Consequently, non-plasma methods for removing photoresist, residue, and other contaminants from semiconductor substrates are needed.
Conventional non-plasma methods for removal of, for example, post-etch photoresist and polymer residue (especially over low-k dielectrics) present numerous challenges. Traditional wet chemical cleaning methods use solvents such as NMP, along with amines (e.g., hydroxylamine) to strip resist and remove sidewall residue. However, such wet solvent processes require a deionized (DI) water rinse to remove traces of solvent from the features that have been etched into the dielectric. As feature sizes are reduced, and their aspect ratio increases, penetration of DI water and liquid solvents into these features becomes more difficult due to surface tension issues. Also, if liquids do penetrate into such small features, then it becomes increasingly difficult to subsequently remove. Consequently, wet processes have limitations in cleaning residue from the bottom of high-aspect ratio features with small lateral dimensions. Additionally, these wet cleaning methods can over etch exposed layers. This can cause device reliability problems or lead to nonfunctional circuits. And although the oxidative chemistry component of some traditional wet clean methods (e.g. dilute HF (50:1-1000:1 HF:H2O) or xe2x80x9chot Piranhaxe2x80x9d (90% H2SO4/10% H2O2)) can be effective at cleaving the bonding structures of contaminant residues, often the formulations and or cleaning conditions do not provide efficient physical removal of the contaminants. These methods also have the disadvantage of requiring handling and exposure to corrosive and flammable media, thus requiring extensive abatement and environmental controls.
Also, there are a number of emerging methods for cleaning wafers, such as densified fluids. Densified fluids are good solvents for contaminants and residues resulting from semiconductor fabrication. Some of these processes, especially those conducted at supercritical pressures, employ additives to increase the solvating power of the process fluid itself. Other additives are used to remove specific contaminants such as polymers, organics, metals, and the like. Although supercritical fluids hold promise for wafer processing, more can be done to exploit their valuable physical properties.
During such processes, a UV light may be used to generate free radicals to facilitate photoresist and post etch residue removal. During such processes, UV light is supplied to a supercritical process vessel via a high pressure window in a wall of the supercritical process vessel. The UV light passes through the window to illuminate an area adjacent to the wafer. One problem with this approach is that the window needs to be thick enough and strong enough to survive supercritical pressures; such windows attenuate some of the UV light. Also, by having the UV source outside of the vessel, thorough exposure of the workpiece is problematic.
It is desirable to provide a supercritical process vessel that provides improved UV irradiation of a wafer surface.
To achieve the foregoing and in accordance with the purpose of the present invention, a method for processing a wafer is provided. The wafer is placed within a supercritical process vessel. A light source is activated, where the light source is within the supercritical process vessel. A supercritical fluid is introduced into the supercritical process vessel, where the light source is exposed to the supercritical fluid.
In another embodiment of the invention, an apparatus for processing a wafer is provided. A supercritical process vessel with an interior for holding a supercritical fluid is provided. A wafer support for supporting a wafer within the interior of a supercritical process vessel to expose the wafer to the supercritical fluid is provided. A lamp, which is able to operate at supercritical fluid pressures within the interior of the supercritical process vessel to expose the lamp to the supercritical fluid is provided.